Shock absorber with welded piston

ABSTRACT

A piston and piston rod assembly for use in a hydraulic shock absorber of the direct acting type has an open ended piston with a base having a flat weld surface thereon fixedly secured to the end of a piston rod. Rebound and compression valving are secured in the open end of the piston and flow passageways are formed in the base of the piston in close non-interference relationship with the weld surface on the piston base. The piston and piston rod are connected by an improved method which maintains flow paths in the connected parts.

United States Patent [191 Stormer [54] SHOCK ABSORBER WITH WELDED PISTON[75] Inventor: Joseph R. Stormer, Vandalia, Ohio [73] Assignee: vGeneralMotors Corporation,

Detroit, Mich.

[22] Filed: Feb. 16, 1971 [21] Appl. No.: 115,222

[52] US. Cl ..188/322, 188/317 [51] Int. Cl. ..Fl6t 9/348 [58] Field ofSearch ..188/282, 317, 322

[56] References Cited UNITED ST-ATES PATENTS 1,529,235 3/1925 Bechereau..1ss/2s2 3,187,847 6/1965 Karlgaardmn... ..188/317 7/1968 Rasmussen..188/282 X [111 3,724,615 1 Apr. 3, 1973 FOREIGN PATENTS ORAPPLICATIONS 1,107,155 8/1955 France ..l88/322 Primary Examiner-GeorgeE. A. Halvosa Attorney-W. S. Pettigrew and J. C. Evans [57] ABSTRACTpiston base. The piston and piston rod are connected by an improvedmethod which maintains flow paths in the connected parts.

2 Claims, 9 Drawing Figures PATENTEDAPM I975 SHEET 1 BF 2 ATTORNEY SHOCKABSORBER WITH WELDED PISTON This invention relates to hydraulic shockabsorbers and more particularly to a welded piston and piston rodsub-assembly and the method of manufacture of the sub-assembly.

Piston and piston rod sub-assemblies for use in hydraulic shockabsorbers have been interconnected by means of a threaded stud and nutfasteners and have additionally been interconnected by the use of hotupseat methods wherein a portion of the piston rod is deformed into atight interlocking relationship with the piston. Furthermore, the use ofresistance butt-welding to connect two pieces together is known.

In such arrangements, it is necessary to configure the component partsof the assembly to include adequate provision for the flow of hydraulicfluid from one side to the opposite side of the piston.

Additionally, it is necessary to configure the piston and piston rodcomponents to produce a strong interconnection therebetween withoutinterfering with the hydraulic flow patterns throughout the assembly.

The present invention pertains to'an improved resistance weldedconnection formed by application of a D.C. weld sequence between amodified piston and piston rod configuration to form. a high strengthinterconnection between the component parts and a good hydraulic flowpath from one side to the opposite side of the piston through thepiston.

More particularly, the invention relates to a sub-assembly wherein thepiston has an open end thereon in which are located the valvingcomponents of the piston. Additionally, the piston includes a flatbaseportion having a. weld surface formed concentrically around thelongitudinal axis of the piston against which the butt end of the pistonrod is welded. The piston base portion includes an annular dam whichseparates the weld surface from a non-restricted flow area through the.base which freely directs hydraulic fluid fromthe valving components onone side of the piston to the opposite side of the piston.

An object of. the present invention is to provide a stronginterconnection between the piston and piston rod of .a hydraulic shockabsorber by the provision of a flat welding surface and a separating damthereon against which the butt end of a piston rod is fixedly secured bythe application of a pressure weld sequence.

Another object of the present invention is to improve amethodfor weldinga shock absorber piston to a piston .rod by forming thev piston to havea base with peripheral flow openings therethrough, undercutting the baseof an open ended piston to form a flat weld surface thereon surroundedby the flow openings, thereaftersecuring a peripheral seal on the pistonrod and then concentrically locating a weld surface on the end of apiston rod with respect to the outer diameter of thesealon the peripheryof the piston and thereafter applying a controlled pressure and D.C.electric current across the aligned and interconnected piston rod andpiston to weld the parts together without weld splatter and to deformthe weld end of the piston rod to fill an undercut surface on the pistonwithout encroachingupon the flow openings through the piston.

Still another object of the present invention is to provideaweldedpiston and piston. rod assembly for a shock absorber which includes aclosed center piston base. portion @formed concentrically of thelongitudinal axis of the piston and piston rod with an annular, outerperipheral dam thereon which separates heat and pressure deformedportions on the piston rod that are welded to the closed center base onthe piston from inclined flow passageways through the piston into avalve chamber formed within the open end of the piston.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein a preferred embodiment of the present invention isclearly shown.

IN THE FIGS.:

FIG. 1 is an exploded view of the component parts of the piston andpiston rod assembly prior to assembly;

FIG. 2 is a vertical cross-sectional view of a cold formed piston blank;

FIG. 3 is a diagrammatic view of a plurality of process steps whereinthe piston blank is undercut to form a weld surface on the base thereofand a seal seat on the periphery thereof;

FIG. 4 is a view in vertical section showing the seal in place on theperiphery of the piston;

FIG. 5 is a fragmentary end view of a piston rodprior to connection tothe piston;

FIG. 6 is a view in vertical section showing a fixture arrangement forconcentrically locating the pistoh with respect to the outer diameter ofthe seal on the piston in preparation to formation of a weldtherebetween;

FIG. 7 is a view in vertical section showing the con centrically alignedpiston seal, and piston rod andth welding position of the piston rod andpiston along with electrodes for applying a D.C. weld current sequencebetween the piston and piston rod;

FIG. 8 is a view in vertical section of thewe lded piston rod, thepiston and valve components prior toassembly; and i FIG. 9 is a viewlike FIG. 8 with the valving com ponents located within the piston.

Referring now to the drawings, in FIG. 1, an exploded sub-assembly of ashock absorber is ilhistrated which includes a piston rod 20 having aweld'e'nd 22 thereon.

A piston 24 is illustrated which is adapted to: welded to the end 22 ofthe rod 20. The-piston 24 is a hollow open ended member in which arelocateda compression intake valve spring 26 and anannular compressionintake valve member 28. A They are supported on one end of an orificeplate30."

mounting ring 37 and a cover plate 39.

The aforementioned exploded components are" util ized in practicing thenoval and improved method of the present invention and are configured toproducean improved, novel piston and piston rod sub-assembly for use inhydraulic shock absorbers.

The method of the present invention first includes the step of coldforminga wire slug into the shape of a hollow opened piston blank 38 asillustrated inFIGfZ.

The blank includes a base portion 40 andanop en ended flange 42 thereon.

Further, the blank includes a flat annular internal surface 44 which isconcentrically arranged with respect to bevelled internal annularsurface 46 between surface 44 and flange 42.

The next step of the method includes a sequence of metal cutting stepsincluding the following:

The piston is undercut to form a closed center weld surface 48 on thebase 40. Additionally, an annular dam 50 is formed between the surface48 and a plurality of flow openings 52 which are formed through the base40 and are located in concentric relationship with the weld surface 48.

Additionally, the hollow interior of the piston 38 is formed by asuitable cutting tool 54 to have a recess with an inclined surface 56which intersects the openings 52 to provide a large unrestricted flowarea 58 at the intersection between each opening 52 and the surface 56.The angle of this surface and that of surface 57 on the outside of baseportion 40 minimize production problems by allowing drilling into andbreaking out on surfaces perpendicular to the drill center duringformation of openings 52. Additionally, the tool 54 serves to finish theannular shoulder 44 and the interior bevelled surface 46.

Another step in the metal forming sequence is that of forming an annularseal seat 60 on the outer periphery of the piston 38 by means of a tool62.

The seal seat 60 extends from the flange 42 to a point adjacent the base40 and is formed continuously around the outer surface of the piston 38as illustrated in FIG. 3.

It is adapted to supportingly receive a sleeve formed nylon seal member64 which is mounted on the piston 38 by being located concentricallytherewith and then being slipped over the base 40 of the piston 38 intoretained engagement with the seal seat 60.

The next step in the method includes the step of locating the completedpiston and seal assembly 66 with respect to the piston rod 20.

As illustrated in FIG. 5, the piston rod component has a tip portion 68thereon formed on the end of a spherical weld production 70.

The projection 70 then merges with a second tapered portion 72 that hasa lesser inclination and which is joined to the straight wall portionsof the rod 20, at a circumferential transition 74 where the rod hasstraight walls.

The positioning step of the invention includes locating the outerdiameter of the straight wall portion of the rod 20 concentrically withrespect to the outer diameter of the seal member 64.

More particularly, this is accomplished by means of a fixture whichincludes a base 76 and a hardened steel locating jaw 78 having anopening 80 thcrethrough in which is located the straight wall portionsof the rod 20. The opening 80 in the jaws 78 is maintained in closeconcentricity with an opening 82 in an expanding collett 84, which has ahead 86 and a base 88 adjustably supported on the base 76 for calibratedmovement with respect to the jaws 78 and the opening 80 therein.

The piston and seal sub-assembly 66 is supported within the opening 82of collett 88 which engages the OD of the seal 64 to maintain it inclose concentric relationship with the straight wall portion of the rod20.

In this alignment step, the rod 20 has its longitudinal axis alignedwith respect to the longitudinal axis of piston 38 and furthermore thetip portion 68 on the rod 20 is located generally concentrically withrespect to the flat weld surface 48 on the base 40.

The next step of the method includes locating a first electrode 90 inelectrical contact with the straight wall portion of the piston rod 20and a circular cross section electrode 92 so that flat end surface 94thereon is supportingly received by a flat finished surface 96 on theinside of the base portion 40.

Then the parts are squeezed together by an application of force againstthe rod 20 and the electrode 92.

Once the force is applied, a DC weld power supply 95 is connected acrossthe electrodes and is operated to produce a weld sequence including asqueeze step wherein the parts are pressed together for a predeterminednumber of welding cycles; thereafter, weld current is applied across theelectrodes 90, 92 for a lesser number of weld cycles; the pressure ismaintained on the parts through a quench period and thereafter a lesserweld current is passed across the electrodes during a temper period.

By virtue of the application of pressure and welding current during thewelding sequence, the projection 70 of the rod 20 is forced into theundercut closed center weld surface 48 to till it as the parts are beingintegrally connected by the welding of material in the base 40 to thematerial at the tip of the rod 20.

During this step, the dam 50 prevents plastic flow of molten materialinto the openings 52. This maintains a good open flow path through thecross sectional area of openings 52 at the outer surface of the base 40.The sequence produces a strong weld joint 99 between piston 24 andpiston rod 20.

In one working embodiment, the parts were configured as follows toproduce a strong joint without blockage of openings 52.

Part Dimension Piston 24 OD. Groove 0.965 inch l.D. Surface 48 0.495inch Thickness Base 40 0.190 inch Diameter Hole 52 O.l25 inchInclination Hole 52 20 Rod 20 O.D. 0.489 inch Projection 1.00 inchradius Taper 72 12 0.125 inch The joined piston and piston rod are thenremoved from the aligning and welding fixture and the valving componentsare located within the hollow open end of the piston 24 as shown in FIG.8.

The next step of the method includes locating the separate valvingcomponents within the hollow open end of the piston 38.

More particularly, this includes placing the parts in the alignmentshown in FIG. 1 into the interior of the piston 38 as illustrated inFIG. 8.

In this configuration the spring 26 has a circumferential segment 97supported by the annular shoulder 44 and the orifice plate 30 has abevelled end portion 98 thereon supported by the annular bevelledsurface 46.

The rebound spring 34 holds the valve cage 36 slightly above thesupported parts. Then the cage is moved axially with respect to theflange 42 within the piston 38 so that an annular flange 99 thereon islocated axially within the opened ended flange 42. The flange 42 is thenspun over the valve assembly. The completed assembly is illustrated inFIG. 9.

This article is an improved assembly for. use in hydraulic shockabsorbers.

In addition to including the strong weld joint 96 between piston 38 androd 20, it includes an improved flow path configuration which isprovided by the combination of the inclined surface 56 on the pistonintersecting the openings 52 to provide openings 58 that allowrelatively unrestricted flow from a control chamber 100 located betweenpiston 38 and the interior surface 102 of the orifice plate 30.

Additionally, the openings 52 are inclined at an angle with respect tothe longitudinal axis of the welded piston and piston rod so that fluidflows from the control chamber toward the center of piston 24. There isan unrestricted flow path through chamber 100 and it allows smooth flowin a diverging direction with respect to the rod during itsreciprocation into and out of an oil filled pressure cylinder of a shockabsorber.

The inclination of openings 52 locates them away from the interiorannular shoulder 44 where it supports the compression spring 26. Thesupport is at a point radially outwardly of the unrestricted opening 58to avoid interference between the flow pattern of hydraulic fluid andthe intake valve spring 26. The spring 26 biases the compression intakevalve 28 against annular valve seats 104, 106 that separate a pluralityof compression flow passageways 108 from the control chamber 100 duringa rebound movement, wherein the piston rod moves outwardly of an oilfilled pressure cylinder on the shock absorber.

During this movement, oil flowsfrom the pressure cylinder through theinclined passageway 52 into unrestricted control chamber 100 from whenceoil flows through a rebound opening 110 formed centrally of the orificeplate 30.

The opening 110 is controlled by a rebound valve 1 12 which is moved toan open position which is shown in broken lines in FIG. 9 during therebound movement against the force of the rebound spring 114.

The oil thence flows through an end opening 116 in the cage 36 and sideopening 118 thereon formed at spaced points along an inclined peripheralwall 130 of the cage 36.

During the compression stroke, the rebound valve 1 12 is closed and thecompression valve 104 opens against the force of spring 26. Hydraulicfluid flows in an unrestricted path from the compression chamber throughthe openings in the valve cage thence through the control orifice 108 inthe plate 30 into chamber 100 where the oil freely flows through theinclined openings I 52 and the oblong entrance opening 58 formed by theintersection of surface 56 and the openings 52 and thence radiallyoutwardly of the piston 20 into the rebound chamber of the pressurecylinder.

One representative weld sequence to connect the piston rod and piston ofthe embodiment in FIGS. 1 through 9 includes the following weldsequence:

Weld Force 1230 lbs.

Squeeze 40 cycles Weld Current Max. 30,000 amps.

5 cycles Weld Downslope l0 cycles.

Weld Quench 80 cycles Weld Temper cycles Weld Temper Current 14,400amps.

This weld sequence is merely representative but illustrates a suitablesequence for obtaining the following objectives of the improved method,namely that of filling the undercut weld surface with weld material anddeforming the tapered end of the piston rod 20 into a fused relationshipwith the base 40 without overflowing the annular dam 50 to reduce thecross sectional area of the openings 52 that surround the dam 50.

Furthermore, the weld sequence results in an unusually high strengthbutt weld between the piston and piston rod making the sub-assemblysuitable for use in heavy duty road use shock absorbers.

In the preferred embodiment of the present invention, the weld currentacross the electrodes is direct current. This current reduces splatterof the weld material out of the control region of the undercut surface48 to further reduce the possibility of flowing or otherwise causingmetal to reduce the flow area of the inclined openings 52.

What is claimed is as follows:

1. A combination piston and piston rod assembly for use in a doubledirect-acting hydraulic shock absorber of the type including a pressurecylinder filled with oil comprising: a hollow piston member having abase porbeing inclined with respect to the longitudinal axis of saidpiston rod and serving to direct oil from the rod side of said piston ina converging direction into the center interior of said piston, meansincluding inclined internal surface forming a control chamber withinsaid piston adjacent the base portion thereof, said openingsintersecting with said inclined surface to afford an unrestricted flowpath into said control chamber, an orifice plate located within saidcontrol chamber, a first valving element on one side of said orificeplate, a spring for maintaining said first valving element closed duringa first movement of the piston and piston rod, an annular supportshoulder in said piston at a point radially outward of said chamber, asecond valving element on the opposite side of said orifice plate andspring means on said support shoulder for maintaining said secondvalving element closed during an opposite movement of said piston andsaid piston rod, said spring means and said second valving element beinglocated by said shoulder radially outwardly of said control chamber awayfrom fluid flow centrally therethrough, said orifice plate including afirst and second plurality of openings therein each freely communicatingwith said open control chamber for alloyving flow of fluid from saidcontrol chamber to opposite sides of said orifice plate within saidhollow piston.

2. A combination piston and piston rod assembly for use in a doubledirect-acting hydraulic shock absorber of the type including a pressurecylinder filled with .oil' comprising: a hollow piston member havingalbase portion and an open ended flange portion thereon, said baseportion having a closed center weld surface thereon, an annular damsurrounding said closed center surface, a piston rod having a top weldedin fused relationship with said piston on the closed center weldsurface, a plurality of flow openings directed through said base intothe interior of said hollow piston, said annular dam defining a barrierbetween said weld material at said piston rod and said openings, each ofsaid openings being inclined with respect to the longitudinal axis ofsaid piston rod and serving to direct oil from the rod side of saidpiston in a converging direction into the center interior of saidpiston, means including an inclined internal surface forming a controlchamber within said piston adjacent the base portion thereof, saidopenings intersecting with said inclined surface to afford anunrestricted flow path into said control chamber, an annular supportshoulder in said piston at a point radially outward of said chamber, anorifice plate located within said control chamber, a first valvingelement on one side of said orifice plate, a spring for maintaining saidfirst valving element closed during a first movement of the piston andpiston rod, 21 second valving element on the opposite side of saidorifice plate and spring means on said support shoulder for maintainingsaid second valving element closed during an opposite movement of saidpiston and said piston rod, said spring means and said second valvingelement being located by said shoulder radially outwardly of saidcontrol chamber away from fluid flow centrally therethrough, saidorifice plate including a first and second plurality of openings thereineach freely communicating with said open control chamber for allowingflow of fluid from said control chamber to opposite sides of saidorifice plate within said hollow piston, an inclined outer surface onsaid piston formed continuously around said piston, said flow openingsbeing directed through said outer inclined surface to locate theentrance to the openings on the rod side of the piston away frominterferring fluid flow relationship with the outer surface of saidpiston rod at the point it is welded to said base portion.

1. A combination piston and piston rod assembly for use in a doubledirect-acting hydraulic shock absorber of the type including a pressurecylinder filled with oil comprising: a hollow piston member having abase portion and an open ended flange portion thereon, said base portionhaving a closed center weld surface thereon, an annular dam surroundingsaid closed center surface, a piston rod having a tip welded in fusedrelationship with said piston on the closed center weld surface, aplurality of flow openings directed through said base into the interiorof said hollow piston, said annular dam defining a barrier between weldmaterial at said piston rod and said openings, each of said openingsbeing inclined with respect to the longitudinal axis of said piston rodand serving to direct oil from the rod side of said piston in aconverging direction into the center interior of said piston, meansincluding an inclined internal surface forming a control chamber withinsaid piston adjacent the base portion thereof, said openingsintersecting with said inclined surface to afford an unrestricted flowpath into said control chamber, an orifice plate located within saidcontrol chamber, a first valving element on one side of said orificeplate, a spring for maintaining said first valving element closed duringa first movement of the piston and piston rod, an annular supportshoulder in said piston at a point radially outward of said chamber, asecond valving element on the opposite side of said orifice plate andspring means on said support shoulder for maintaining said secondvalving element closed during an opposite movement of said pIston andsaid piston rod, said spring means and said second valving element beinglocated by said shoulder radially outwardly of said control chamber awayfrom fluid flow centrally therethrough, said orifice plate including afirst and second plurality of openings therein each freely communicatingwith said open control chamber for allowing flow of fluid from saidcontrol chamber to opposite sides of said orifice plate within saidhollow piston.
 2. A combination piston and piston rod assembly for usein a double direct-acting hydraulic shock absorber of the type includinga pressure cylinder filled with oil comprising: a hollow piston memberhaving a base portion and an open ended flange portion thereon, saidbase portion having a closed center weld surface thereon, an annular damsurrounding said closed center surface, a piston rod having a top weldedin fused relationship with said piston on the closed center weldsurface, a plurality of flow openings directed through said base intothe interior of said hollow piston, said annular dam defining a barrierbetween said weld material at said piston rod and said openings, each ofsaid openings being inclined with respect to the longitudinal axis ofsaid piston rod and serving to direct oil from the rod side of saidpiston in a converging direction into the center interior of saidpiston, means including an inclined internal surface forming a controlchamber within said piston adjacent the base portion thereof, saidopenings intersecting with said inclined surface to afford anunrestricted flow path into said control chamber, an annular supportshoulder in said piston at a point radially outward of said chamber, anorifice plate located within said control chamber, a first valvingelement on one side of said orifice plate, a spring for maintaining saidfirst valving element closed during a first movement of the piston andpiston rod, a second valving element on the opposite side of saidorifice plate and spring means on said support shoulder for maintainingsaid second valving element closed during an opposite movement of saidpiston and said piston rod, said spring means and said second valvingelement being located by said shoulder radially outwardly of saidcontrol chamber away from fluid flow centrally therethrough, saidorifice plate including a first and second plurality of openings thereineach freely communicating with said open control chamber for allowingflow of fluid from said control chamber to opposite sides of saidorifice plate within said hollow piston, an inclined outer surface onsaid piston formed continuously around said piston, said flow openingsbeing directed through said outer inclined surface to locate theentrance to the openings on the rod side of the piston away frominterferring fluid flow relationship with the outer surface of saidpiston rod at the point it is welded to said base portion.